A standard modular shelf arrangement is formed by ladder-like uprights that are connected together by shelves that are normally seated on metal rods fitted into holes in these uprights or they are fixed onto these uprights by means of dovetail formations. By using uprights and shelves of different sizes as well as further accessories like intermediate shelves, doors, drawers and the like it is possible to put together virtually any conceivable type of unit, of virtually any desired height or width. On the other hand such arrangements have the considerable disadvantage that they cannot be extended perpendicularly, and even for a simple setup it is necessary to use a great number of different elements that must be expensively manufactured to high tolerances.
Another known type uses grooved bars that fit together and that can be fitted with thin panels to form box-like shelves. Such arrangements offer very little flexibility and their parts must be made to very close tolerances. Furthermore it is also impossible to extend this type of unit perpendicularly.
The base of another known type of modular furniture is formed by two pairs of panels two of which are provided on at least one of their longitudinal edges with a series of notches so that they can form the uprights of the assembly and two of which are provided at their ends with notches so they can be used as shelves. These notches fit together so that the panels can be locked together and built up into a three-dimensional structure. Such elements must be very carefully manufactured, and also do not permit the piece of furniture to be extended or added to perpendicular to its main direction of elongation.